This invention relates generally to polarizers, and, more particularly to polarizers which are adjustable, and, therefore, reliably operable over a wide range of wavelengths, i.e., from the ultra-violet through the infrared portion of the optical spectrum.
Polarized light is one of the most useful mechanisms known for studying the characteristics of materials. In many areas, such as in the testing of laser windows, for example, it is of utmost important to analyze the material to be used prior to its actual use. In so doing, catastrophic results can be avoided and the overall cost of a project greatly reduced.
Polarized light is light which has its electric vector oriented in a predictable fashion with respect to the propagation direction while unpolarized light has the vector oriented in a random, unpredictable fashion. It is also generally acknowledged that it is the electric vector rather than the magnetic vector of a light wave that is responsible for the effects of polarization and other observed phenomena associated with light. Therefore, the electric vector of a light wave, for all practical purposes, is considered the light vector.
One of the simplest ways of producing poloarized light is by reflection from a dielectric surface. At a particular angle of incidence, the reflectivity for light whose electric vector is in the plane of incidence becomes zero. The reflected light is thus linearly polarized at right angles to the plane of incidence. Brewster's law states that at the polarizing angle the refracted ray makes an angle of 90.degree. with the reflected ray. By combining this relationship with Snell's law of refraction, it is found that tan i=n where i is the angle of incidence and n is the refractive index. This provides a simple way of measuring refractive indices.
Generally polarizers are constructed of dichroic crystals such as Tourmaline or birefringent crystals such as transparent calcite (Icelandic spar). Unfortunately, there are no practical crystals that are capable of polarizing light in the infrared range as well as polarizing light over a wide range of the optical spectrum. Since diamonds (which are capable of polarizing light in the infrared range) are too expensive to use as polarizers and other polarizers heretofore in use generally are too inaccurate, within the infrared range, for the precision required in many of the testing procedures used today, a need has arisen for polarizers which are useable with light in the infrared portion of the optical spectrum.